In a tire mounted on a vehicle, heat generated during rotation of the tire has heretofore been a problem. An increase in temperature of the tire due to heat generation leads to acceleration of change over time such as changes in physical properties of a tire material, breakage of a tread during high-speed driving, and the like. Particularly, in an off-the-road radial (ORR) tire and a truck bus radial (TBR) tire, friction with a rim flange and upthrust from the rim flange deforms rubber in a tire side section, particularly, on a bead section side, and thus heat is more likely to be generated. Heat generated in the tire side section accelerates deterioration of the rubber, leading to deterioration in not only durability of the bead section but also durability of the tire. There has been a demand for a tire capable of suppressing an increase in temperature on the bead section side of the tire side section.
In a tire described in Patent Literature 1, for example, a turbulence generation protrusion is formed along a tire radial direction within a predetermined range of a tire side section, as means for suppressing an increase in temperature of a bead section. Thus, turbulence having a high flow rate is generated on a surface of a tire to facilitate heat release from the tire side section, thereby suppressing the increase in temperature on the bead section side.
Incidentally, the conventional tire described above has the following problem. Specifically, a method including formation of protrusions in the tire side section increases the volume of rubber in the tire side section. As a result, heat is more likely to be generated due to an increase in deformation amount of the rubber during rotation of the tire. In other words, the effect of suppressing temperature increase by facilitating heat release with formation of protrusions is deteriorated. Moreover, since rubber is required to form the protrusions, an increase in amount of rubber required for a pneumatic tire increases production cost. For these reasons, further improvement has been desired for the tire suppressing the increase in temperature of the tire side section, particularly on the bead section side.